Recently, mobile equipments such as a cellular phone and a PDA (Personal Digital Assistance) have been used for various purposes at various locations, and new products have been developed one after another. A reflective-transmissive type liquid crystal display (hereinafter, referred to as “transflective liquid crystal display”) is an example of a liquid crystal display that is often used in these equipments. The transflective liquid crystal display has capabilities of both a reflective type display that uses reflection of strong ambient light such as sunlight from a reflector and a transmissive type display that uses transmitted light from an illumination device such as a backlight. The transflective liquid crystal display can be used at various locations. Therefore, technology of the transflective liquid crystal display has been actively developed and various technologies and ideas have been applied to display panels.
FIG. 13 is a schematic cross-sectional view of a currently widely used transflective liquid crystal display. As shown in FIG. 13, in the transflective liquid crystal display, a transparent electrode 101 for a transmitting portion for transmitting light 301 from an internal backlight therethrough and a reflector 102 for reflecting external light 302 are provided in a single pixel. The reflector 102 is produced by forming an electrically conductive metal having a high reflectance such as Al and Ag on an interlayer insulating film 103 having a finely corrugated profile, and is used as an electrode for a reflective portion. The corrugated profile of the reflector 102 is precisely designed with photolithography technology or the like so that the reflector 102 efficiently reflects incident light 302 and improved brightness and improved reflection display characteristics are obtained.
In the transflective display, an optical path length of the light 302 reflected from the reflector 102 in the reflecting portion is different from that of the internal light 301 in the transmitting portion. Therefore, various techniques are required to obtain equal display capability both in the reflecting portion and the transmitting portion. In particular, since color design is a very important display property. Since light 302 passes through the color filter 201 twice in a reflection display mode, color adjustment between the transmitting portion and the reflecting portion is implemented by making the color purity of a color filter 201 in the reflecting portion smaller than that of a color filter 202 in the transmitting portion, changing the color filter thickness between the reflecting portion and the transmitting portion, and the like.
High quality screen has been increasingly demanded not only for large screen displays but for small screen displays used for mobile equipments, and very high definition displays of more than 200 ppi (pixel per inch) have been developed for mobile equipments. However, since higher definition displays have a smaller pixel size, a large margin for misalignment needs to be set in the manufacturing process, which reduces an aperture ratio (a ratio of display size to pixel size). In a liquid crystal display element, large misalignment is caused in the process of bonding a thin film transistor (TFT) substrate and a counter substrate having a color filter to each other. This large misalignment has been a problem in manufacturing a high definition display. Therefore, so-called CF on TFT technology, a technology of forming a color filter (CF) directly on a TFT substrate, has been developed instead of the currently used method of forming a color filter on a counter substrate (for example, see Patent document 1).
Recently, a lightweight, flexible plastic substrate has attracted attention for use in next-generation displays. A plastic substrate changes in dimensions significantly by temperature and water compared to a glass substrate. Therefore, the CF on TFT technology that does not cause misalignment in the bonding process is an especially promising method for manufacturing a flexible display using a plastic substrate.
Patent document 1: Japanese Patent Laid-Open Publication No. 8-122824